About two-thirds of the Earth's surface is covered by clouds at any given time. An increasing number of LEO spacecraft systems are intended to obtain imagery data of features on the ground that may be obscured by such clouds. In the absence of real-time knowledge of cloud location, LEO system resources may be wasted as a result of collecting and processing image data that are unusable as a result of cloud obscuration. Knowledge of where clouds are in real or near real time would mitigate this problem. Low latency is important, because cloud coverage can drastically change in a timeframe of a few minutes (cloud speed 30-100 mph). Referring now to FIG. 7, a comparison of Detail A and Detail B, images obtained one hour apart, demonstrates how significantly cloud coverage patterns change in the space of one hour.
The assignee of the present invention manufactures and deploys spacecraft that provide communications and broadcast services, many of which operate from geosynchronous orbits (GEO), that is, circular, near-equatorial orbits having a radius of 42,164 kilometers. The Geo orbit has an orbital period of one sidereal day, thus a satellite in GEO (a “GEO spacecraft”) appears nearly stationary to a ground station on the earth, which is advantageous for many communications and broadcast mission. GEO spacecraft, as the term is used herein and in the claims, include spacecraft disposed in geosynchronous orbits having an inclination as high as 15 degrees. Communications or broadcast satellites, as the term is used herein and in the claims, include only spacecraft having a primary radiofrequency (RF) payload drawing 10 kW or more.
A satellite in GEO can persistently obtain image data of a substantial fraction of the Earth's surface. Although some current GEO satellites include a primary payload configured to obtain image data for weather forecasting purposes, for example, ground processing of the image data can take several hours. Moreover, the cost to deploy a GEO satellite having an imaging system suitable for weather forecasting as a primary payload satellite is extremely high. Thus, such systems tend to be developed as national/regional assets, e.g., the US Geostationary Operational Environmental Satellite (GOES) system, the Japanese Geostationary Meteorological Satellite (GMS) system, and Multifunctional Transport Satellites (MTSAT), and the European Meteosat program.